1. Field of the Invention
The present invention relates to a base station, an upper node, a radio communication system and a radio communication method for allocating radio resource to uplink data.
2. Description of the Related Art
Heretofore, a radio communication system including base stations and radio network controllers has been known. The base station has one or multiple cells which each perform radio communication with a radio terminal. The radio network controller manages multiple base stations and allocates radio resource to radio terminals. Note that such a technique (referred to below as first technique) is sometimes called R99 (Release 99).
Recently, for improved throughput, shorter delay time and the like, a technique has been proposed in which a base station (network side) performs operations such as allocation of radio resource to uplink data transmitted from a radio terminal to the base station. Note that such a technique (referred to below as second technique) is sometimes called HSUPA (high speed uplink packet access) or EUL (enhanced uplink).
Each cell functions as a serving cell or a non-serving cell depending on the case. A transmission rate of uplink data (such as a TBS (transport block size) determined according to an SG (scheduling grant)) is controlled by using transmission rate control data transmitted from a serving cell and a non-serving cell. Transmission rate control data includes absolute transmission rate control data (AG; absolute grant) for directly specifying the transmission rate and relative transmission rate control data (RG; relative grant) for relatively specifying the transmission rate (see 3GPP TS25. 321 Ver. 7.5.0, for example).
Here, uplink data is transmitted from the radio terminal to the base station through an enhanced dedicated physical data channel (E-DPDCH). Absolute transmission rate control data (AG) is transmitted from the base station to the radio terminal through an absolute transmission rate control channel (E-AGCH; E-DCH absolute grant channel). Relative transmission rate control data (RG) is transmitted from the base station to the radio terminal through a relative transmission rate control channel (E-RGCH; E-DCH relative grant channel).
A serving cell transmits absolute transmission rate control data (AG) and relative transmission rate control data (RG) to a radio terminal. Meanwhile, a non-serving cell transmits only relative transmission rate control data (RG) to a radio terminal, and does not transmit absolute transmission rata control data (AG).
The above-mentioned base station according to the second technique includes a call reception control unit configured to control whether or not to receive a new call, and a scheduling unit configured to control radio resource (transmission rate) to be allocated to uplink data. The scheduling unit transmits absolute transmission rate control data (AG) or relative transmission rate control data (RG). There are two types of transmission time interval (TTI) for uplink data different in the length of 1 TTI, which are 2 msec TTI and 10 msec TTI. In the case of 2 msec TTI, the scheduling unit can transmit absolute transmission rate control data (AG) or relative transmission rate control data (RG) at each TTI.
Here, the call reception control unit controls whether or not to receive a new call depending on the radio resource (transmission rate) allocated to the radio terminal. For this reason, the call reception control unit needs to acquire a radio resource allocation state from the scheduling unit. For example, the call reception control unit may make an inquiry about the radio resource allocation state to the scheduling unit, in response to a new call-establishment request.
However, making the inquiry about the radio resource allocation state lowers the speed of processing for receiving new calls. On the other hand, without making the inquiry about the radio resource allocation state, the call reception control unit cannot know the radio resource allocation state in real-time, and hence cannot appropriately control reception of new calls.
Furthermore, calls based on 2 msec TTI include a call for which the scheduling unit controls radio resource allocation at each TTI. If the scheduling unit controls radio resource allocation at each TTI, the call reception control unit cannot know the radio resource allocation state in real-time and thus cannot appropriately control reception of new calls.